(Verschlussabstand): The space available for the cartridge between the face of the breechblock and the part of the chamber that keeps the cartridge from going forward. A critical dimension.
The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.
The fit of a cartridge in a chamber measured as the distance from breech face to that part of the chamber which stops the cases forward movement. Insufficient headspace hinders complete chambering; excessive headspace permits case stretching or separation.